Bead area durability is one of the concerns of the tire industry. A conventional tire bead portion 100 is illustrated in prior art FIG. 4. What is conventionally considered the main portion 104 of a carcass reinforcing ply extends radially inward toward the tire rim and is turned about an inextensible bead core 106 to form a carcass ply turnup 108. The carcass ply turn up 108 extends at a single angle μ relative to a radial line tangent to the axially outermost point of the bead core 106 and parallel to the tire equatorial plane.
Due to the configuration and nature of the radial carcass, when a tire is expanded, the main portion of the carcass is put under tension, pulling the carcass main portion 104 radially upward and the carcass turn up 108 radially inward. After inflation and during operation of the tire, when the tire is under deflection, the carcass ply is subject to bending forces and the carcass main portion 104 moves radially inward while the carcass turnup 108 moves radially and axially outward. During both tension and deflection, the rubber surrounding the carcass main portion 104 and the carcass turn up 108, due to the adhesion relationship between the rubber and the reinforcing cords of the ply, also is forced to move and the rubber is stressed. The movement of the carcass ply and the surrounding rubber may result in cracking of the rubber in the tire bead portion, decreasing durability of the tire.
Other attempts have been made to improve the durability of the bead portion. U.S. Pat. No. 6,260,597 (Miyazono) discloses a pneumatic tire having multiple organic fiber cord reinforced layers in the bead portions outward of a carcass ply. Axially outward of the carcass ply turnup, the terminal ends of the organic fiber layers are all at the same height or radially outward of the terminal end of the carcass ply turnup. Because the axially outer organic fiber layers are predominately radially outward of the carcass ply terminal end, when the bead portion is subjected to strain during operation, it is the organic fiber layer ends that are subjected to the greater load and where crack initiation may begin, resulting in reduced bead durability. Miyazono teaches that to improve durability, the ends of the organic fiber layers are bent in various different embodiments while the carcass ply turnup is maintained at a single angle.
Several prior art patents similarly propose applying textile cord layers adjacent the turnup ends of a pneumatic tire to improve durability as in U.S. Pat. No. 4,234,029 and U.S. Pat. No. 4,093,014 having a folded over U shaped chipper. U.S. Pat. No. 6,962,183 uses an axially outer short steel cord chipper terminating radially below the turnup end wherein both the chipper and the turnup end are covered by a nylon patch.
In U.S. Pat. No. 4,842,033 gum strips are proposed to cover the turnup ends to improve durability.
In U.S. Pat. No. 6,962,183 and U.S. Pat. No. 6,877,538 the use of an axially outer steel or organic cord reinforced chipper layer is taught wherein the outer end terminates below preferably well below the high ply turnup terminal end which is encased in insulation rubber.
All of these exemplary prior art patents where attempts to improve tire bead area durability and to reduce crack propagation which is a common issue in heavy duty commercial truck tires, particularly such tires using a steel reinforced carcass ply.